This application claims Paris Convention priority of Japanese Application No. Hei 11-189100 filed Jul. 2, 1999 and International Application No. PCT/JP00/04376 filed Jun. 30, 2000, the complete disclosure of which are hereby incorporated by reference.
The present invention relates to a SOI (Silicon-On-Insulator) substrate including a silicon substrate and an insulating layer buried in the silicon substrate, and to a manufacturing method therefor. More particularly, the present invention relates to a SOI substrate manufactured by a SIMOX (Separation by Implanted Oxygen) technique and a manufacturing method therefor, as well as a semiconductor device utilizing the SOI substrate.
The SIMOX method as one of SOI substrate manufacturing methods is to bury an insulating layer into a silicon substrate. Concretely, as shown in FIG. 8(a), the SOI substrate 1 is obtained by dosing oxygen ions at a higher concentration into a silicon substrate 2, and thereafter annealing the silicon substrate 2 at a higher temperature to thereby form a buried silicon oxide layer 3 in a region at a predetermined depth from the surface of the silicon substrate 2, in which a SOI layer 2a at the top surface side of the layer 3 is used as an active area.
However, cross-sectional end peripheries 3a, 3a of the buried silicon oxide layer 3 of the SOI substrate 1 are not buried within the substrate, and are exposed at substrate side surfaces. Thus, upon etching during a semiconductor device manufacturing process such as by a hydrofluoric acid aqueous solution, the exposed end peripheries 3a, 3a of the oxide layer 3 are removed by etching. As a result, those cross-sectional end surfaces 2b of the SOI layer 2a corresponding to an upper layer are brought into an overhung state like a canopy, as shown in FIG. 8(b). Since these overhung portions 2b, 2b have such a small thickness on the order of 0.05 to 0.3 xcexcm, these portions are poor in mechanical strength and are chipped and/or peeled off during subsequent processes. Silicon fragments caused thereby become particles which adhere onto the surface of the SOI layer 2a as the active area. Devices formed on the SOI layer 2a having adhered particles lead to a cause of defects such as of patterning and in various deposition films, thereby problematically lowering a product yield.
As a SIMOX method to improve such a problem, there has been known a manufacturing method of a semiconductor substrate in which cross-sectional both end surfaces of a silicon substrate are coated by a resist, and oxygen ions are dosed from the exposed main surface of the silicon substrate into the interior of the silicon substrate to thereby form a buried silicon oxide layer within the silicon substrate (Japanese Patent Application Laid-Open No. HEI-129267(129267/1992)).
In the manufacturing method of a semiconductor substrate according to the aforementioned conventional SIMOX method, however, ion dosing is performed in a state where the resist exists at both end surfaces. Thus, those ions having higher energies also impinge the resist constituted of organic matters containing impurities such as metals, so that those organic matters struck out from the resist upon ion dosing tend to spatter to thereby adhere onto the surface of the SOI layer as the active area. This leads to such a problem that the surface of the SOI layer as the active area is contaminated by impurities such as metals.
Meanwhile, silicon substrates are sometimes provided with marking characters thereon, for identifying the substrates themselves. Those marking characters are mainly provided by laser irradiation, and as shown in FIG. 2, marking characters 16a (such as xe2x80x9cABC-XYZxe2x80x9d) are provided in a marking character area 16 at an end periphery of one of the main surfaces of a substrate 11. In manufacturing a SOI substrate 1 shown in FIG. 9(b) from a silicon substrate 2 provided with marking characters 4 as shown in FIG. 9(a), oxygen ions I are dosed into the interior of the silicon substrate 2 similarly to the aforementioned SIMOX method, followed by an anneal processing at a higher temperature so as to form a buried silicon oxide layer 3 in a region at a predetermined depth from the surface of the silicon substrate 2. The marking characters by laser irradiation generally reach a depth of about 1 xcexcm from the substrate surface. Further, the buried silicon oxide layer is formed at a sub-micron depth from the substrate surface. Thus, when a SOI substrate is manufactured after providing marking characters at the end periphery of the main surface of the silicon substrate, or, when marking characters are provided at the end periphery of the main surface after the SOI substrate is manufactured in an unshown manner, the marking character portion and the buried oxide layer overlap with each other, thereby causing a problem of dust occurrence from the marking character portion.
It is therefore an object of the present invention to provide a manufacturing method of a SOI substrate, which prevents particles and impurities such as metals in a resist, from adhering onto a SOI layer as an active area, to thereby improve a product yield.
It is another object of the present invention to provide a manufacturing method of an SOI substrate for preventing dust occurrence due to marking characters.
It is yet another object of the present invention to provide a SOI substrate which noway causes dust occurrence due to marking characters.
It is still another object of the present invention to provide a semiconductor device adopting a SOI substrate having extremely lesser adherence such as of particles and impurities onto a SOI layer as an active area.
The invention of claim 1 as shown in FIG. 1 is a manufacturing method of a SOI substrate comprising the steps of: forming an oxide film 12 at cross-sectional both main surfaces and both end surfaces of a silicon substrate 11; forming a resist layer 13 on the oxide film 12 at cross-sectional both end surfaces of the substrate 11; removing the oxide film 12 at those portions which are left from the covering of the resist layer 13, to thereby expose the both main surfaces of the silicon substrate 11; removing the resist layer 13 to thereby leave the oxide film 12 at the both end surfaces of the substrate 11; dosing oxygen ions I into the substrate 11 from one of the exposed both main surfaces, followed by an anneal processing to thereby form an oxide layer 14 in a region at a predetermined depth from the one main surface of the substrate 11; and removing the oxide film 12 left on the both end surfaces of the substrate 11.
According to the invention of claim 1, oxygen ions I are dosed into the exposed silicon substrate 11 in a state where the resist layer 13 is removed from the oxide film 12, and the anneal processing is conducted. Thus, there can be avoided adherence of impurities such as metal into the SOI layer 11a as an active area. Further, since cross-sectional both end surfaces of the silicon substrate 11 are coated by the oxide film 12 upon ion dosing, dust occurrence from the end surfaces of the SOI layer 11a as the active area can be avoided during the subsequent device manufacturing process so that contamination due to particles onto the surface of the device is avoided.
The invention of claim 2 as shown in FIGS. 4 and 5 is a manufacturing method of a SOI substrate of claim 1, wherein the silicon substrate 11 includes a marking character area 16 for carrying marking characters for identifying the substrate 11 at an end periphery of the one of the both main surfaces of the substrate 11, and wherein the resist layer 13 covers the marking character area 16, when the resist layer 13 is formed on the oxide film 12 at the both end surfaces of the substrate 11.
According to the invention of claim 2, since the resist layer 13 covers the marking character area 16, the marking character area 16 is not exposed during the oxide film removing process. Thus, the buried silicon oxide layer 14 is not formed under the marking character area 16, thereby enabling avoidance of dust occurrence due to marking characters.
The invention according to claim 4 as shown in FIG. 6 is a manufacturing method of a SOI substrate comprising the steps of: forming an oxide film 12 at cross-sectional both main surfaces and cross-sectional both end surfaces of a silicon substrate 11; removing the oxide film 12 at one of the both main surfaces of the silicon substrate 11 to thereby expose the one main surface of the substrate 11; dosing oxygen ions I into the substrate 11 from the exposed one main surface, followed by an anneal processing to thereby form an oxide layer 14 in a region at a predetermined depth from the one main surface of the substrate 11; and removing the oxide film 12 left on the other main surface and the both end surfaces of the substrate 11.
The invention of claim 5 is a manufacturing method of a SOI substrate of claim 4, wherein removal of the oxide film 12 on the one main surface of the silicon substrate 11 is conducted by contacting only the one main surface of the silicon substrate 11 with a hydrofluoric acid aqueous solution 21 while rotating the silicon substrate 11.
According to the invention of claim 4 or 5, the process to form the resist layer in the invention according to claim 1 is not required, so that ion dosing is conducted after more readily coating the cross-sectional end surfaces of the substrate.
The invention of claim 6 is a SOI substrate free of a buried silicon oxide layer 14 just under marking characters 16a attached to the substrate surface for substrate identification.
According to the invention of claim 6, the marking characters 16a and the buried silicon oxide layer 14 never overlap with each other, thereby avoiding dust occurrence due to marking characters.
The invention of claim 7 is a semiconductor device adopting a SOI substrate free of a buried silicon oxide layer 14 just under marking characters 16a attached to the substrate surface for substrate identification.
The invention of claim 8 is a semiconductor device adopting a SOI substrate manufactured by a method of claim 1 or 3.
The invention of claim 9 is a semiconductor device adopting a SOI substrate manufactured by a method of claim 4 or 5.
According to the invention of anyone of claims 7 through 9, the semiconductor device adopts a SOI substrate having extremely lesser adherence such as of particles and impurities onto a SOI layer as an active area, leading to extremely lesser defects such as of patterning and in various deposition films.